+ Explicitly request the read-the-docs style.
  Running locally has always required us to request `sphinx_rtd_theme`.
  Previously, readthedocs.org would use its eponymous style (`sphinx_rtd_theme`) by default.
  This appears to have changed, so request `sphinx_rtd_theme` no matter where we are running.
+ Remove references to the breathe python module since it is unused.
+ Remove some useless whitepace.